The present invention relates to a hydraulic brake system for automotive vehicles operable by independent force which includes a master brake cylinder preceded by a hydraulic brake force booster that has a booster piston and a working chamber to which an auxiliary pressure source is connectable, wherein a valve device operable by way of an electromagnetic drive is provided which establishes a hydraulic connection between the working chamber and an unpressurized pressure fluid supply reservoir in a first switching position and a connection between the working chamber and the auxiliary pressure source in a second switching position.
A brake system of this type is disclosed in German patent No. 32 41 662, for example. Preferably, the valve device of the prior art brake system comprises one normally open and one normally closed electromagnetic valve which are configured as digitally operated valves which are actuated by maximum openings of different length (pulse width modulation) and, thus, are less appropriate for controlling or dosing the hydraulic pressure introduced into the working chamber.